Venus surface images Options

[ngunn]

I have a question arising from the recent surface images acquired by the Parker Solar Probe (but best discussed in this section, I think, if anyone has comments). Would a camera with similar specifications to WISPR but located on Earth or in Earth orbit be able in principle to image the night-side surface? It presents quite a large target when suitably placed and I imagine some sort of coronagraph arrangement could be used to exclude light from the sunlit crescent.
EDIT - link reposted here: https://www.nasa.gov/feature/goddard/2021/p...g-view-of-venus

[scalbers]

If measurements were accurate enough the surface emissivity could be studied.

[JRehling]

It took me a while to find these but a couple of amateurs (really straining the definition of the word) have posted their nightside images of Venus here.

These were taken from Australia with a 20" telescope (amateur!) by Phil Miles with occasional collaboration mentioned in his posts by one or more others.

http://www.astrogem.com.au/Venus/nightside-2020/

It's wildly impressive but still falls short of what can be done from space, of course. And even an Earth-orbiting satellite is hamstrung by the rotational synchrony: You can only image certain portions of Venus well (about 20%-25% of it) when it's a waning crescent, and another 20-25% when it's a waxing crescent, and such observations are only possible for about 1 month out of every 19.

From the Earth's surface, such observations are limited by the scant minutes per day. There are only about 20-30 minutes per day to image the thin crescent and gathering all the light you can with all the IR you can capture fills that 20-30 minutes pretty well. Amateurs are typically imaging with a filter that blocks out everything shorter than about 1 micron (900 nm might work). On the longer end of wavelengths, the filter might allow no real limit but the camera itself, as well as the atmosphere of Venus dim out the signal so you're probably effectively imaging off about a 100nm wide band. Trying to get a multispectral signal for a fancy emissivity study by slicing up your spectrum would probably eliminate the signal to noise. And, as I mentioned, the long IR wavelengths mean a much harsher diffraction limit on your resolution, even if your scope is in space.

Of course, either Veritas or EnVision would be making such observations from Venus orbit and I think that's a dataset much to be desired. Until we make such observations, it is still speculative what science can be had because there's a need to compensate for [Venus] atmospheric interference with the surface signal and the richness of the surface signal itself depends upon the mineralogy of Venus, which is out of our hands, and the thing that we'd like to investigate. But the preliminary work done with Venus Express data is convincing that this dataset is worthwhile… yet to be seen is how worthwhile.

This is part of why I've been crossing my fingers throughout the last two Discovery selections for Venus to get its first U.S. mission since Magellan.